1. Field of the Invention
The present invention relates to a developing apparatus to be employed in an electronic photograph recorder or an electrostatic duplicator, and the like, particularly to a developing apparatus for supplying a developer from a supply roller to a developing roller, and further delivering the developer to an electrostatic latent image on a carrier, thereby to develop the image.
2. Description of the Prior Art
There are various conventional methods for delivering a toner as a developer to an electrostatic latent image carrier in an electronic photograph recorder and the like, e.g. as disclosed in Japanese Patent Laid-Open Publication No. 63-231469 which employs a developing roller alone as the toner delivery means. Another known system employs, in addition to the developing roller, a delivery or supply roller that first delivers the toner to the developing roller that thereafter delivers the toner to the electrostatic latent image carrier.
In the latter developing apparatus, the supply roller for delivering the toner normally is disposed substantially beneath a toner hopper storing the toner therein, and the toner dropped from the toner hopper is supplied to a developing roller. A restricting or doctor blade contacts the developing roller and restricts the thickness of the toner layer on the surface of the developing roller. The blade is urged toward contact with the developing roller under pressure by a spring. The toner layer of restricted thickness is delivered to the electrostatic latent image carrier by the rotation of the developing roller per se, and hence the latent image is developed.
Since the supply roller supplies toner dropped thereon from the toner hopper and accumulated thereon, the amount of toner to be supplied to the developing roller is large, and the toner layer on the developing roller composed of a large amount of toner is thinned by the blade. The toner that is removed or stopped by the blade is residual and is maintained in a reservoir disposed upstream of the delivery direction. During the course of developing process, the amount of toner in the reservoir is increased and will fully occupy the entire space of the reservoir. Further supply the toner into the reservoir when it is fully occupied by toner permits the blade to push or lift upwardly from the surface of the developing roller against the resilient force of the spring due to the pressure of the toner. Consequently, there will be a space between the surface of the developing roller and the tip end of the blade, and there is a likelihood that the layer of the toner restricted by the blade will be undesirably thick. Furthermore, there is a likelihood that the toner will be compressed and solidified by such pressure of the toner, such that toner particles having large diameters will be delivered to the developing position. For these reasons, there have occurred such problems that the substrate on which the image is developed is contaminated, suitable resolution cannot be obtained, and surplus toner is absorbed by the electrostatic latent image carrier at the time of developing.